1. Field of Invention
The present invention relates to compositions containing sulfur hexafluoride, methods of using the same, and devices and articles of manufacture comprising the compositions.
2. Description of Related Art
Perfluorocarbon compounds (PFC's), hydrofluorocarbon compounds (HFC's), chlorofluorocarbons (CFC's), hydrochlorofluorocarbon compounds (HCFC's), and sulfur hexafluoride (SF6) are widely used in a variety of industrial, commercial, consumer and public use applications and uses. However, several of these compounds have been identified as particularly problematic to the environment in that they contribute to the greenhouse gas effect, i.e., they have relatively high global warming potentials (GWP). For example, SF6 possesses one of the highest GWP values of known compounds.
Due to its relatively high GWP, SF6 is being phased out of several applications for which low-GWP substitutes are available. However, presently there is no adequate substitute for SF6 when used as a gaseous dielectric medium in high voltage (≧1 kV) applications, such as circuit breakers, switchgear, and other electrical equipment. In such devices, pressurized SF6 is used as a gas-phase insulator because it has much higher dielectric strength compared to several other available compounds such as air or dry nitrogen. Although the electrical industry has taken steps to reduce the leak rates of SF6 from high voltage equipment, monitor SF6 usage, increase recycling of equipment utilizing SF6, and generally reduce SF6 emissions to the atmosphere, it would still be advantageous to find a SF6 substitute for electrical applications utilizing a dielectric gas.
In addition to electrical applications, relatively low GWP substitutes for SF6 are desirable for other applications such as refrigeration, closed cell foam production, propellants for sprayable compositions, magnesium cover gases, and the like. There is particularly a need for such new compositions that are essentially non-flammable, that do not have a deleterious effect on the atmosphere, that are chemically stable, and that have high dielectric strength. For example, new low GWP compositions designed for use as refrigerants or blowing agents should preferably have similar stability as existing refrigerants or blowing agents, be non-flammable, and have a normal boiling point within a reasonable range as existing refrigerants or blowing agents.
While a number of compositions have been proposed as suitable substitutes for high GPW compositions, compounds were heretofore unknown that have an acceptable combination of boiling point, chemical stability, low GWP, non-flammability, and acceptable performance as a refrigerant, blowing agent, and/or high-voltage dielectric gas. For example, carbon dioxide is a refrigerant that is stable and has a relatively low GWP, but the vapor pressure of this compound are significantly higher than most refrigerants now in use. This deficiency generates significant problems in attempting to implement its use in the refrigeration industry because existing refrigeration equipment would have to be extensively modified, redesigned, or replaced to utilize CO2 as a refrigerant. Thus, there is still a significant need to develop a composition or mixture of compositions that have an acceptable combination of boiling point, chemical stability, low GWP, non-flammability and dielectric performance.